Method of concentrating aqueous hydrazine



United States Patent i METHOD OF CONCENTRATING AQUEOUS HYDRAZINE Oscar J. Swenson, Crystal Lake, and Don W. Ryker,

Alton, 111., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Application April 2, 1953, Serial No. 346,513

18 Claims. (Cl. 202-57) This invention relates to an improved process for the manufacture of hydrazine and particularly to substantially anhydrous hydrazine, i e. a product containing at least about 95% hydrazine by weight. This application is a continuation in part of co-pending application Serial No. 156,046, filed February 14, 1950, and now abandoned.

Hydrazine, as ordinarily manufactured, is obtained in relatively dilute aqueous solution. Hydrazine and water form .a constant boiling mixture so that the dilute solutions obtained cannot be concentrated by ordinary fractional distillation to a hydrazine content greater than about 64% to 70%. In order to obtain higher concentrations of hydrazine by further distillation it is necessary to include in the distilland a dehydrating agent, such as sodium hydroxide, barium oxide, or calcium oxide. In order to obtain higher yields of substantially anhydrous hydrazine and to avoid the hazards of explosion occasioned by high distillation temperatures, such further distillation is carried out at reduced pressure. However, even with such precaution explosions occur. In the absence of oxygen, hydrazine will, under suitable circumstances, decompose violently. Such explosions may be attributed to the presence of small amounts of impurities such as iron oxide, electric sparks, and the like which initiate the autodecomposition of the hydrazine.

It is therefore an object of this invention to provide a safer method for manufacturing hydrazine. It is another object of the invention to provide an economical process for safely producing hydrazine of high concentration without the requirement of reduced pressure during distillation. A further object is to provide an improved economical efiicieut method for producing substantially anhydrous hydrazine. A still further object is to render hydrazine vapor sufficiently insensitive to elec tric sparks and the like that mass decomposition thereof is prevented. It is still another object of this invention to provide a safer method for handling and storing hydrazine and to provide the novel product resulting from such method.

The foregoing objects and advantages are attained in accordance with this invention by desensitizing hydrazine with a hydrocarbon. This is accomplished by distilling 2,774,725 Patented Dec. 18, 1956 ICC of an upper layer of liquid rich in hydrazine and a lower layer of liquid rich in sodium hydroxide monohydrate. Although ,the hydrazine may be distilled directly from this mixture, if desired these liquid layers may be separated prior to distillation, with the upper layer being subsequently distilled to recover the hydrazine. The hydrocarbon is included during the distillation process in accordance with this invention and a saturated hydrocarbon having a boiling point in the range of about 90 C. to 175 C. at atmospheric pressure is preferred. While,.as pointed out in the co-pending application referred to hereinbefore, saturated hydrocarbons boiling in the range of about 90 C. to 150 C. are particularly suited for the purpose, it has now been found that hydrocarbons having a boiling point at atmospheric pressure as high as 175 C. may be utilized successfully in even lesser amounts without reaching a distillation temperature at atmospheric pressure engendering hazard from hydrazine decomposition. While hydrocarbons having a boiling point in the range of 150 C. to 175 C. are distilled over in a lesser amount, due totheir lower vapor pressure, the amount is still sufiicient to prevent violent decomposition of the hydrazine in the event of a spark or the like and such hydrocarbons are advantageous be cause they may be used in lesser amount. When the mixture is distilled, the distillate is composed of substantially anhydrous hydrazine and the hydrocarbon. Inasmuch as the liquid hydrocarbon is immiscible with the hydrazine, the distillate separates into two layers and the hydrocarbon layer may be decanted and returned for reuse in concentrating more hydrazine.

It has been found that the hydrazine solution may be distilled safely at atmospheric pressure due to the fact that in the presence of the hydrocarbon the hydrazine distills over at a lower temperature and the fact that the amount of such hydrocarbon vaporized with the hydrazine is sufiicient to prevent violent decomposition of the hydrazine, thereby greatly reducing the explosive hazard. Any hydrocarbon which is saturated and boils within the range of about 90 C. to 175 C. at atmospheric pressure is satisfactory for the purpose. Such hydrocarbons are exemplified by the paraflins, cyclo- 2,4,4-trimethylhexane;

the aqueous hydrazine solution in contact with a dehydrating agent and the hydrocarbon. Sodium hydroxide is the preferred dehydrating agent although barium hydroxide, calcium oxide and the like may be tane;

parafiins, and their isomers having the general formula Caln+2 or 01,112", in which n is an integer, and boiling within the range of about C. to C. Representativeexamples are normal heptane; normal octane; n-decane; Z-methylnonane; 2,7-dimethyloctane; 2,3,6-trimethylheptane; Z-methylheptane; 3-methylheptane; 4- methylheptane; cycloheptane; nonane; 2,4-dimethylheptane; Z-methyloctane; 2,5-dimethylheptane; 2,6-dimethylheptane; 4-ethylheptane; 3-methyloctane; 4-rnethyloctane; 2,2,4-trimethylpentane, 2,2,3,3-tetramethylbutane; 3-ethylpentane; 3-ethyl-2-methylpentane; 3-ethyl-3-rnethylpentane; 2,3-dimethylhexane; 2,4-dimethylhexane; 2,5-dimethylhexane; 3,4-dimethylhexane; 3-ethylhexane; 2- methylhexane; 3-methylhexane; 2,2,5-trimethylhexane;

3,3-diethylpentane; methylpentane; 2,2,3,4-tetramethylpentane; 2,2,4,4-tetramethylpentane; 2,3,3,4-tetramethylpentane; ethylcyclopentane; 1,Z-dimethylcyclopentane; 1,3-dimethylcyclopentane; n-propylcyclopentane; isopropylcyclopentane; 1- methyl-l-ethylcyclopentane; 1-methyl-cis-2-ethylcyclopen- 1,1,Z-trimethylcyclopentane; 1,1,3-trimethylcyclopentaneg 1,1-dimethylcyc1ohexane; and 1,1,3-trimethylcyclohexane. Mixtures of such hydrocarbons may likewise be utilized to good advantage. Low cost commercially available mixtures of saturated hydrocarbons ob- 2,2,3,3-tetrataincd by fractionation of petroleum crude oils are also suitable. For instance, typical analysis of such cornmercially available hydrocarbons are:

Suitable mixtures of saturated hydrocarbons obtained by fractionation of petroleum crude oils and boiling in the range between 143 C. and 175 C. are also available. It will be noted that such commercially available saturated hydrocarbons may contain minor amounts of unsaturated aromatics, which in such amounts are permissible. Unsaturated aromatic hydrocarbons, in general however, are not suited for the purpose due to their tendency to react with the hydrazine. Ordinarily such reaction involves hydrogenation of the aromatic with the conversion thereof to a saturated hydrocarbon with a resulting loss in yield of hydrazine. In situations where it is an economy to use a saturated hydrocarbon which is contaminated with substantial proportions of unsaturated compounds, at a sacrifice in the yield of substantially anhydrous hydrazine, such impure saturated hydrocarbons may, of course, be used.

Hydrocarbons having a boiling point substantially above 175 C. are not satisfactory for the purpose due to their low vapor pressure and insuflicient amount distilled over to prevent decomposition of the hydrazine. Hydrocarbons having a boiling point substantially below about 90 C. are not in general suited for the purpose due to the impractically large amount of such hydrocarbon distilled over with a given amount of hydrazine. Minor amounts of such higher and lower boiling hydrocarbons may, of course, be included in a hydrocarbon mixture for the purpose, provided the resulting mixture boils within the range of about 90 C. to about 175 C.

The amount of the saturated hydrocarbon distilled over with the hydrazine will, of course, vary with different hydrocarbons but the preferred hydrocarbons boiling in the range from 90 C. to 175 C. distill over in ample amount to prevent hazardous decomposition of the accompanying hydrazine. For instance, Table II shows for representative hydrocarbons in the first column, the approximate boiling temperature of the pure hydrocarbon; in the second colrunn, the average temperature attained during distillation of the hydrazine when distilling at atmospheric pressure a mixture of the aqueous hydrazine, sodium hydroxide and the hydrocarbon; in the third column, the minimum mole percent of the hydrocarbon in a mixture of the hydrocarbon vapor and hydrazine vapor effective to prevent mass decomposition of the hydrazine; and in the fourth column, the mole percent of hydrocarbon in the mixture of substantially anhydrous hydrazine and hydrocarbon vapors actually distilled over at atmospheric pressure. For example, Table II shows that a vapor mixture containing 13% n-heptane and 87% hydrazine is not sensitive to mass decomposition from the action of electric sparks and the like, and further that such a vapor mixture containing greater than 13% n-heptane is likewise insensitive whereas lesser amounts are hazardous. The Table 11 further shows, for example, that the vapor distilled from a mixture of aqueous hydrazine, n-heptane, and sodium hydroxide (present in amount equimolar with the water) is composed of approximately 69% n-heptane and 31% substantially anhydrous hydrazine, all such percentages being calculated in mole percent. The ratio of n-heptane to hydrazine in the distillate is therefore advantageously greater than the permissible minimum ratio represented by the 13% content of n-heptane. The per- 4 missible minimum for decane is 9.6% but as will be noted the amount of decane actually distilled over, namely 15%, is ample to prevent such mass decomposition.

Table II Hydrocarbon-Hydrazine Vapor Mixture Boiling Average Tempera- Boiling ture of Tempera- Minimum Hydroture of of Hydro- Hydrocarbon, Mixture, carbon Percarbon in 0. C. missible, Distillate,

Mole Mole Percent Percent n-heptanc 98. 5 83 13.0 69 2,2,4-trin1ethylpentanc 99. 3 85 15. 5 62 n'oetane 125.8 13. 3 4% Petroleum fraction 121-143 103. 5 20. 0 3o n-nonanc... 150.7 108 11. O 25 n-decane. 174. 0 109. 5 9. c 15. 5

When an electric spark was passed through a vapor composed of hydrazine and less than the minimum percent of hydrocarbon shown in Table 11, column 3, a violent explosion occurred, whereas no explosion or fire occurred with mixtures in which the hydrocarbon content was greater than the minimum. It has been found that the ratio of hydrocarbon to substantially anhydrous hydrazine distilled over remains during distillation, for all practical purposes, approximately constant for each hydrocarbon and it will be apparent from a comparison of the mole percent distilled over, shown in the fourth column, with the mole percent necessary to prevent decomposition of the hydrazine, shown in the third column, that the amount of each hydrocarbon distilled over is amply suificient to prevent mass decomposition of the hydrazine. In fact, the amount is sufficient to prevent mass explosion even in the presence of small amounts of air. In the absence of the hydrocarbon even a small amount of air in the hydrazine vapor is sufl'icient at elevated temperature to initiate a violent explosion.

Inasmuch as the hydrocarbon, hydrazine, and sodium hydroxide monohydrate exist within the still substantially as separate layers of liquid and inasmuch as the hydrazine and hydrocarbon exist as separate layers in the distillate, the process is well suited for continuous operation. Such continuous operation may be accomplished for instance, by continuously feeding the dilute aqueous hydrazine, sodium hydroxide and hydrocarbon to the still while continuously removing sodium hydroxide monohydrate from the still and separately removing the hydrocarbon and hydrazine from the distillate receiver. The hydrocarbon from the distillate can be fed continuously back into the still and a portion of the sodium hydroxide monohydrate solution removed from the still can be enriched with sodium hydroxide to serve as the sodium hydroxide fed to the still with the aqueous hydrazine. The amount of sodium hydroxide monohydrate removed from the system depends upon the amount of water fed to the still in the aqueous hydrazine solution and such sodium hydroxide monohydrate may be dehydrated to recover sodium hydroxide, which anhydrous material can then be returned to the still and the cycle continued.

When it is desired to store or ship the substantially anhydrous hydrazine in containers having a vapor space above the liquid level, the decomposition hazard therein can be advantageously reduced in accordance with this invention by including therewith some of the hydrocarbon.

Having thus described the invention in a general way, the invention will be further clarified by the following specific example:

To '500 parts by Weight of an aqueous solution containing 54.5% of hydnazi-ne in a suit-able distilling vessel there were added 523 parts by weight of 97% sodium hydroxide and 200 parts by weight of a hydrocarbon composed of a commercially available mixture obtained by fractionation of crude oils and having a boiling range of 121 C. to 143 C. The composition was as shown hereinbefore in Table I. The sodium hydroxide water molecular ratio was thus about 1 to -1. Heat was then applied to the distilling vessel to b'rmg the mixture quickly to boiling temperature, approximately 1103.5 C., and distillation was continued until the temperature raised to 107 C. at which point substantially all of the hydrazine had been collected in the distillate. Some of the hydrocarbon was in the still throughout distillation. The substantially anhydrous hydrazine was sepairated from the hydrocarbon in the distillate by decantation and was found to represent 99% of the original hydrazine and had :a hydrazine concentration of 96.3 .v

The composition of the vapor distilled off in the foregoing example was such that electric sparks and the like could not bring about mass decomposition of the hydrazine vapor. The amount of hydrocarbon vapor was suflicient to prevent any hazard of fire or explosion even with the presence of small amounts of air. 7

Instead of adding an excess of liquid hydrocarbon to the still, as described in the foregoing embodiment, the hydrocarbon may be metered as a vapor into the still in sufiicient amount to prevent autodecomposition of the hydrazine vapor, but the use of the liquid in excess of the amount distilled over is preferred. In such operation some liquid hydrocarbon should be maintained in the still throughout the distillation.

In another embodiment, to 500 parts by Weight of an aqueous solution containing 54.5% of hydrazine in a suitable distilling vessel there were added S23 parts .by weight of 97% sodium hydroxide and 200 partsby weight of decane. The sodium hydroxide-water molecular ratio was thus about 1 to 1. Heat was then applied to the distilling vessel to bring the mixture quickly to boiling temperature, approximately 108 C., and distillation was continued until the temperature raised to 110 C. at which point substantially all of the hydrazine had been collected in the distillate. Some of the hydrocarbon was in the still throughout distillation. The substantially anhydrous hydrazine was separated from the hydrocarbon in the distillate by decantation and was found to rep-resent 95% of the original hydrazine and had a hydrazine concentration of 95.5%.

From the foregoing description it should be apparent that the present invention accomplishes its objects and provides a safe economical process for producing substantially anhydrous hydrazine from dilute aqueous solutions of hydrazine. Although rather specific conditions for effecting the manufacture of hydrazine in accordance with this invention are set forth in the foregoing examples, it is to be understood that the invention is not limited to the exact temperatures nor to the ingredients, or other details, set forth therein, except as indicated by the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In the process of concentrating aqueous hydrazine, the step which comprises distilling said hydrazine in contact with a dehydrating agent and a saturated hydrocarbon whose boiling temperature at atmospheric pressure is within the range of about 90 C. to 175 C., said hydroc'ar-bon being present in an amount sufiicient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

2. The method of desensitizing hydrazine vapors which comprises maintaining the hydrazine vapor in intimate contact with saturated hydrocarbon vapor, condensing the vapors, and separating the hydrazine from the hydrocarbon condensate, said hydrocarbon having a boiling temperature at atmospheric pressure within the range of about 90 C. to 175 C.

3. In the process of concentrating aqueous hydrazine the step which comprises distilling said hydrazine in contact with a dehydrating agent and a saturated hydrocarhon whose boiling temperature at atmospheric-pressure is within the range of about C. to 175 C. while maintaining some of said hydrocarbon in the distilland throughout the distillation, said hydrocarbon being present in an amount sufficient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

4. In the process of concentrating aqueous hydrazine the step which comprises distilling said hydrazine in contact with sodium hydroxide and a saturated hydrocarbon whose boiling temperature at atmospheric pressure is within the ran-geof about 90 C. to 175 C., said hydrocarbon being present in an amount suflicient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

5. In the process of concentrating aqueous hydrazine the step which comprises distilling said hydrazine in contact with. sodium hydroxide and a "saturated hydrocarbon having a boiling temperature at atmospheric pressure within the range of about 90 C. to 175 C. while maintaining some of said hydrocarbon in the distilland throughout the distillation, said hydrocarbon being present in an amount suflicient to maintain the vapor of said hydrocarbon in intimate contact with the evolved bydrazine vapor throughout the distillation.

-6. *In the manufacture of hydrazine, the steps of concentrating aqueous hydrazine which comprise distilling a mixture of aqueous hydrazine, a dehydrating agent, and a saturated hydrocarbon having a boiling temperature at atmospheric pressure within the range of about 90 C. to 175 C. until substantially all the hydrazine has been removed from the -mixture while maintaining some of said hydrocarbon in the mixture throughout the distillation, collecting the distillate and mechanically separating the layer of hydrocarbon from the layer of hydrazine in saiddistillate, said hydrocarbon being present in an amount suificient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

7. In the manufacture of substantially anhydrous hydrazine, the process of concentrating dilute aqueous hydrazinesolution which comprises intermix-ing an aqueous hydrazine solution with sodium hydroxide in the proportion of at least one mole of sodium hydroxide (for each mole of water to be removed and including therewith a saturated hydrocarbon having a boiling temperature within the range of about 90 C. to 175 C., distilling the mixture until substantially all of the hydrazine has been collected in the distillate while maintaining some out said hydrocarbon in the mixture throughout the distillation, and mechanically separating the substantially anhydrous hydrazine and the hydrocarbon in the distillate.

8. The process in accordance with claim 3 in which the hydrocarbon is a fraction of petroleum crude oil having a boiling temperature at atmospheric pressure within the range of about 90 C. to 175 C.

9. In the process of concentrating aqueous hydrazine, the step which comprises distilling said hydrazine in contact with a dehydrating agent and a saturated hydrocarbon whose boiling temperature at atmospheric pressure is within the range of about 90 C. to C., said hydrocarbon being present in an amount sufiicient to maintain the vapor ,of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

10. The method of desensitizi-ng hydrazine vapors which comprises maintaining the hydrazine vapor in intimate contact with saturated hydrocarbon vapor, condensing the vapors, and separating the hydrazine from the hydrocarbon condensate, said hydrocarbon having a boiling temperature at atmospheric pressure within the range of about 90 C. to 150 C.

11. -In the process of concentrating aqueous hydrazine the step which comprises distilling said hydrazine in con- A tact with a dehydrating agent and :a saturated hydrocarbon Whose boiling temperature at atmospheric pressure is Within the range of about 90 C. to 150 C. while maintaining some of said hydrocarbon in the dist-illand throughout the distillation, said hydrocarbon being pres ent in an amount sufficient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

12. In the process of concentrating aqueous hydrazine the step which comprises distilling said hydrazine in contact with sodium hydroxide and a saturated hydrocarbon whose boiling temperature at atmospheric pressure is within the range of about 90 C. to 150 C., said hydrocarbon being present in an amount sufiici'ent to maintain the vapor of said hydrocarbon .in intimate contact with the evolved hydrazine vapor throughout the distillation,

13. In the process of concentrating aqueous hydrazine the step Which comprises distilling said hydrazine in .contact with sodium hydroxide and a saturated hydrocarbon having a boiling temperature at atmospheric pressure within the range of about 90 C. to 150 C. while maintaining some of said hydrocarbon in the distilland throughout the distillation, said hydrocarbon being present in an amount sufficient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

14. In the manufacture of hydrazine, the steps of concentrating aqueous hydrazine which comprise distilling a mixture of aqueous hydrazine, a dehydrating agent, and -a saturated hydrocarbon having a Iboiling temperature at atmospheric pressure Within the range of about 90 C. to 150 C. until substantially all the hydrazine has been removed from the mixture While maintaining some of said hydrocarbon in the mixture throughout the distillation, collecting the distillate and mechanically separating the layer of hydrocarbon from the layer of hydrazine in said distillate, said hydrocarbon being present in an amount suflicient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

.15. In the manufacture of substantially anhydrous hydrazine, the process of concentrating dilute aqueous hydraziine solution which comprises intewrmixing an aqueous hydrazine solution with sodium hydroxide in the proportion of at least one mole of sodium hydroxide for each mole of Water to be removed and including therewith a saturated hydrocarbon having a boiling temperature Within the range of about C. to C., distilling the mixture until substantially all of the hydrazine has been collected in the distillate While maintaining some of said hydrocarbon in the mixture throughout the distillation, and mechanically separating the substantially anhydrous hydrazine and the hydrocarbon in the distillate, said hydrocarbon being present in an amount sufficient to maintain the vapor of said hydrocarbon in intimate contact with the evolved hydrazine vapor throughout the distillation.

16. The process in accordance with claim 1"1 in which the hydrocarbon is a fraction of petroleum crude oil having a boiling temperature at atmospheric pressure within the range of about 90 C. to 150 C.-

17. The process of desens-itizing hydrazine vapor which comprises maintaining said vapor in intimate contact with a saturated hydrocarbon vapor, said hydrocarbon having a boiling temperature at atmospheric pressure Within the range of about 90 C. to C.

18. The process of desensitizing hydrazine vapor which comprises maintaining said vapor in intimate contact with a saturated hydrocarbon vapor, said hydrocarbon having a boiling temperature at atmospheric pressure Withinthe range of about 90 C. to 150 C.

References Cited in the tile of this patent UNITED STATES PATENTS 500,773 Perelli-Minetti July 4, 1893 1,633,029 Maclntyre Mar. 9, 1920 1,455,072 Buc May 15, 1923 1,985,491 Fisher Dec. 25, 1934 2,077,469 Fazel Apr. 20, 1937 2,471,986 Waddill May 31, 1949 2,485,542 Abrams Oct. 25, 1949 2,493,031 Reid et a1. Jan. 3, .1950 2,567,791 'Schwarcz Jan. 9, 1951 2,690,378 Penneman Sept. '28, 1954 2,698,286 Bircher Dec. 28, 1954 

1. IN THE PROCESS OF CONCENTRATING AQUEOUS HYDRAZINE, THE STEP WHICH COMPRISES DISTILLING SIA DHYDRAZINE IN CONTACT WITH A DEHYDRATING AGENT AND A SATURATED HYDROCARBON WHOSE BOILING TEMPERATURE AT ATMOSPHERIC PRESSURE IS WITHIN THE RANGE OF ABOUT 90* C. TO 175* C., SAID HYDROCARBON BEING PRESENT IN AN AMOUNT SUFFICIENT TO MAINTAIN THE VAPOR OF SAID HYDROCARBON IN INTIMATE CONTACT WITH THE EVOLVED HYDRAZINE VAPOR THROUGHOUT THE DISTILLATION. 